Johne's disease is a chronic diarrheal enteric disease in ruminants that is caused by Mycobacterium avium subspecies paratuberculosis (MAP)(Johne & Frothingham (1895) Dtsch. Zeitschr. Tiermed. Vergl. Pathol. 21:438-454). Live MAP is shed into the milk of cows with Johne's disease (Sweeney (1996) Vet. Clin. North Am. Food Anim. Pract. 12(2):305-12). MAP has been cultured from commercially available pasteurized milk in Europe and the United States (Grant (1998) Appl. Environ. Microbiol. 64(7):2760-1; Ellingson, et al. (2005) J. Food Prot. 68(5):966-72). When Crohn's disease was first described (Crohn, et al. (1932) J. Amer. Med. Assoc. 99:1323-1328), similarities to Johne's disease were identified (Dalziel (1913) Br. Med. J. ii:1068-1070). However, in humans MAP exists in the cell wall-deficient form (Chiodini (1987) J. Clin. Microbiol. 25:796-801). Therefore, in the early analysis of Crohn's disease, MAP could not be detected in humans by the mycobacterial identification techniques of the time, because such techniques stained the mycobacterial cell wall (Ziehl (1882) Dtsch. Med. Wschr. 8:451; Neelsen (1883) Zbl. Med. Wiss. 21:497-501). However, since 1913 the presence of MAP has been identified in humans by other means (see, e.g., Greenstein (2003) Lancet Infect. Dis. 3(8):507-14) and an infectious etiology has been posited for some (Hermon-Taylor (1998) Ital. J. Gastroenterol. Hepatol. 30(6):607-10; Borody, et al. (2002) Dig. Liver Dis. 34(1):29-38), or all (Greenstein (2005) Genetics, Barrier Function, Immunologic & Microbial Pathways. Munster, Germany:25) of inflammatory bowel disease (IBD).
Since the first detection of MAP RNA (Mishina, et al. (1996) Proc. Natl. Acad. Sci. USA 93(18):9816-9820), MAP has been suggested as being the primary and unique, etiological agent of all IBD (Naser, et al. (2004) Lancet 364(9439):1039-1044; Autschbach, et al. (2005) Gut 54(7):944-9; Greenstein (2005) supra; Greenstein (2005) Genetics, Barrier Function, Immunologic & Microbial Pathways. Munster, Germany:24; Greenstein (2005) Crohn's and Colitis Foundation (CCFA) National Research and Clinical Conference. Fourth Annual Advances in Inflammatory Bowel Disease. Miami, Fla.:211) including Perforating and Non-perforating Crohn's disease (Greenstein, et al. (1988) GUT 29:588-592; Gilberts, et al. (1994) Proc. Natl. Acad. Sci. USA 91(126):12721-12724) and ulcerative colitis. It is believed that the particular clinical presentation of IBD that manifests is dependent upon the infected individual's immune response to MAP (Gilberts, et al. (1994) supra). This is analogous to another mycobacterial disease, leprosy. There are two clinical forms of leprosy, tuberculoid and lepromatous (Hansen (1874) Norsk Magazin Laegevidenskaben 4:1-88), both of which are caused by the same organism, M. leprae. The form of leprosy that manifests in a given individual is determined by the immune response of the infected patient (Yamamura, et al. (1991) Science 254:277-279), not by the phenotype or genotype of the leprosy bacillus. 
It has been suggested that Koch's postulates (Koch (1882) Berl. Klin. Wschr. 19:221-230), originally promulgated for use in demonstrating tuberculosis infection, may have been met for MAP in Crohn's disease (Greenstein (2003) supra) and more recently for MAP in ulcerative colitis (Greenstein (2005) supra; Naser, et al. (2004) supra).
The link between MAP infection and other diseases is under investigation. An association between ulcerative colitis and Multiple Sclerosis has been suggested (Rang, et al. (1982) The Lancet pg. 555) and the positive association between IBD incidence rates and Multiple Sclerosis has led to the suggestion that these two chronic, immunologically-mediated diseases may have a common environmental etiology (Green, et al. (2006) Am. J. Epidemiol. 164(7):615-23). However, the common causal agent of ulcerative colitis and Multiple Sclerosis was not identified. Moreover, while the symptoms of Multiple Sclerosis have been ameliorated with variety of therapeutic agents including azathioprine, methotrexate, cyclophosphamide and mitoxantrone (Kaffaroni, et al. (2006) Neurol. Sci. 27 Suppl. 1:S13-7), which have been suggested to mediate the secondary inflammatory response, there has been no indication that these agents affect the primary etiological agent.
There is increasingly compelling evidence that MAP may be zoonotic (Greenstein & Collins (2004) Lancet 364(9432):396-7) and a human pathogen in gastrointestinal disease (Greenstein (2005) supra) and other diseases as well. There is an additional indication that in man, MAP is systemic and not confined to the gastrointestinal tract (Naser, et al. (2000) Am. J. Gastroenterol. 95(4):1094-5; Naser, et al. (2004) Lancet 364(9439):1039-1044). It is suggested that the reason MAP is zoonotic and has been missed as an etiological agent is that the medical profession has been unknowingly treating MAP with anti-inflammatory agents (e.g., 5-amino salicylic acid, methotrexate, and 6-mercaptopurine), which in fact have anti-MAP activity (Greenstein, et al. (2007) PLoS ONE 2:e161; Greenstein, et al. American Society of Microbiology 2007, Toronto, Canada). It is therefore of concern that viable MAP is found in the food chain (Eltholth, et al. (2009) J. Appl. Microbiol. 107:1061-1071), including pasteurized milk (Ellingson, et al. (2005) supra), and potable chlorinated municipal water (Mishina, et al. (1996) Proc. Natl. Acad. Sci. USA 93:9816-9820).
Accordingly, from the perspective of both animal and human health, control of Johne's disease is desirable. However, governmental agencies have been reluctant to initiate global Johne's disease vaccination programs over concern for the loss of ability to diagnose tuberculosis using skin testing.